The present invention relates to a semiconductor device having a wiring layer made of a metal or a metal laminate, and a method of manufacturing such a semiconductor device, and more specifically, to a semiconductor having a wiring layer containing a refractory metal, and a method of manufacturing such a device.
In the method of manufacturing an MOS (metal oxide semiconductor) type integrated circuit, some damages are caused to an end portion of a gate due to RIE (reactive ion etching), ion injection, stress or the like. In order to lessen such damages, it is conventionally considered that an oxidization step should be provided. A gate electrode containing polycrystalline silicon can be oxidized as the electrode is heated in an atmosphere containing dry oxygen or water vapor.
In the meantime, in order to realize a semiconductor device having a fine size and operating at high speed, the development of a metal gate electrode made of a single layer having a low resistance (to be called "metal gate electrode") or a gate electrode having a laminate structure of metal and polycrystalline silicon (to be called polymetal gate electrode) and the like, is presently being progressed.
However, in the oxidizing atmosphere described above, the metal is more easily oxidized than silicon due to the difference between them in the formation energy of an oxide. Thus, the oxidizing rate for metal is very high, and therefore a gate electrode containing metal changes its shape such as the peeling off of the film, due to volume expansion.
In order to avoid this problem, a technique has been proposed (Jnp. Pat. Appln. KOKAI Publication No. 60-9166), for selectively oxidizing silicon only without oxidizing metal by heating an electrode in a mixture gas of water vapor serving as oxidizing agent, and hydrogen serving as reducing agent.
However, according to the researches made by the inventors of the present invention, it has been found that when a metal gate electrode made of a refractory metal such as W or Mo, or a polymetal gate electrode containing a refractory metal such as W or Mo, is subjected to a heat process carried out in an atmosphere containing hydrogen and water vapor, the width of a metal electrode portion is reduced, or the layer is thinned. In the case of a polymetal gate electrode, the cross section of the electrode is decreased, and therefore the resistance value is increased. In the case of a metal gate electrode, not only the resistance value is increased, but also the effective gate length is decreased, and therefore the electrical characteristics of the product would not have appropriate values as designed.
Further, it has been found that if a heat process is carried out at a temperature of 800 to 900.degree. C., not only the decrease in the width or thinning of the electrode occurs, but also whiskers are created on the surface of a metal wiring. The whiskers, in some cases, have a length of several hundred nano-meters. As a result, an interlayer insulation film or the like cannot be deposited uniformly, and such non-uniformed deposition may become a cause for short-circuiting or leakage of current.